High-speed high-power r-f switching



NOV. 9, 1965 RUSSELL 3,217,272

HIGH-SPEED HIGH-POWER R-F SWITCHING Filed May 16, 19 1 3 Sheets-Sheet 1 /0&

PICK-OFF AMPLIFIER FIGI 1 INVENTOR. LINDSAY RUSSELL ATTORNEYS Nov. 9, 1965 I 1.. RUSSELL 3,217,272

HIGH-SPEED HIGH-POWER R-F SWITCHING Filed May 16, 1961 3 Sheets-Sheet 2 32 2a flu POWER SUPPLY TRANSMITTER POWER IN LOAD2 INVENTOR.

LIN DSAY RUSSELL ATTOR N EYS Nov. 9, 1965 RUSSELL 3,217,272

HIGH-SPEED HIGH-POWER R-F SWITCHING Filed May 16, 1961 5 Sheets-Sheet 3 FIGS TRANSMITTER INVENTOR.

LINDSAY RUSSELL wi wkm w m ATTORNEYS United States Patent 3,217,272 HIGH-SPEED HIGH-POWER R-F SWITCHING Lindsay Russell, Cambridge, Mass., assignor to Adams- Russell Co. Inc., Cambridge, Mass., a corporation of Massachusetts Filed May 16, 1961, Ser. No. 110,513 3 Claims. (Cl. 3337) The present invention relates to improvements in the switching of electromagnetic energy and, in one particular aspect, to novel and improved apparatus for control of transmission line characteristics by way of unique ferrite variable reactance devices.

In the guided transfer of UHF or VHF electromagnetic energy from a source to one or more loads, it can be highly important that means be available for the rapid selective switching or direction of the energy flow into different paths. By way of example, the switching of energy from a single high-power transmitter to different ones of a group of antennas is essential in certain scanning systems, and, moreover, such switching must be achieved at exceedingly high speed. Mechanical and other known and conventional devices for controlling energy flow at these frequencies (303,000 me.) and at high power tend to be inefficient, short-lived, and unacceptably sluggish in operation. Preferably, the desired controls over electromagnetic energy flow should instead be independent of mechanical switching motions and should involve simple and wholly electrical and electronic regulation, while at the same time being capable of withstanding intense peak and average transmitting power without serious dissipations, For antenna lobe-switching applications, the de mands are particularly severe in that the switching times be restricted to periods as short as a few milliseconds, and the switching characteristics must remain essentially constant and predictable.

According to the present teachings, the aforesaid purposes are served by apparatus in which known ferrite materials are uniquely exploited in tuned-line sections wherein they afford selective control over the section reactances. Dielectric coolant fluid circulated within these tuned-line sections, in intimate heat-exchange relationship with the ferrite dielectric affords close control over the reactance characteristics, which would otherwise tend to be variable.

It is one of the objects of this invention, therefore, to provide novel and improved apparatus for high-speed switching of high-power R-F energy.

A further object is to provide high-precision variablereactance equipments wherein a magnetically-controlled ferrite and a circulated dielectric fluid closely regulate the effective length of tuned-line sections.

Another object is to provide a novel and improved variable-reactance device, particularly suitable for highspeed switching of R-F energy, which is of relatively simple low-cost construction and which possesses long life under high-power operating conditions.

A still further object is to provide high-precision variable-reactance tuned-line sections in which ferrites operate uniquely to control effective electrical lengths of the sections.

By way of a summary account of practice of this invention in one of its aspects, each of several coaxial waveguide branches feeding a different antenna from a common transmitter output is shunted by a different short-circuited coaxial line section normally exhibiting the high impedance of a quarter-wavelength line or stub. Each such coaxial stub includes an elongated tubular ferrite core intermediate and coaxial with its conductors and, further, a solenoid winding mounted about the exterior of the stub coextensively with the ferrite core. The coaxial conductors and ferrite are spaced to permit circulation of a di- 3,217,272 Patented Nov. 9, 1965 electric temperature-stabilizing fluid, perchlorethylene, axially through the interior of the stub, the stub being sealed against leakage by a suitable dielectric barrier near its open end. Through control of the instantaneous D.-C. currents in the windings, the effective electrical lengths of the coaxial line sections are made to vary, selectably, such that they present either short-circuits or open-circuits to the associated waveguide branches, whereby only one selected antenna may be excited by the transmitter at any moment, for example. Switching of the output to suecessive ones of a group of antennas is readily achieved within a few microseconds. A heat-exchange system associated with the dielectric fluid circulation paths automatically regulates the temperature of the ferrite cores to within substantially a few degrees, and thereby preserves the variable-reactance characteristics of the lines within desired limits.

Although the features of this invention which are believed to be novel are set forth in the appended claims, details as to its organization and method of operation, together with the further objects and advantages thereof, may best be understood through reference to the following description taken in connection with the accompanying drawings, wherein:

FIGURE 1 is a partly sectioned side view of a preferred coaxial switching installation which practices teachings of this invention and in which a ferrite switching line is associated with an auxiliary stub and with automatic temperature-regulating equipment for optimum performance;

FIGURE 2 provides a schematic and block diagram of a simple load-switching arrangement exploiting the im proved switching of this invention;

FIGURE 3 is a diagram of a load-switching arrangement wherein a plurality of improved switching units are present in each branch of a distribution network:

FIGURE 4 is a diagram of a load-switching arrangement wherein power is selectably delivered to any one or more of a plurality of loads; and

FIGURE 5 is a simplified schematic representation of a series arrangement of ferrite line sections for switching between loads.

In the embodiment portrayed in FIGURE 1, a coaxial transmission line 6 is provided for the purpose of propagating high-frequency high-power electromagnetic energy from a source to a load between the cylindrical outer conductor 7 and inner conductor 8. At the illustrated position along this transmission line, a pair of short-circuited coaxial stub units 9 and 10 are inter posed for switching purpose. One of these, unit 9, is of conventional stub construction and is introduced for a resonating purpose described later herein, while the other, unit 10, is uniquely adapted to exhibit different effective electrical lengths as the DC. currents in a surrounding solenoidal winding 11 are changed.

Coaxial line section 10 includes the expected inner cylindrical conductor 12 and a surrounding concentric outer conductor 13 which, together with the shorting plate 14 at the end remote from the junction with line 8, form a shorted line section. These conductors are each fabricated of several parts and thereby facilitate manufacture of a principal portion of the switching line section as a sealed subassembly 10a which may be conveniently attached to the mounting flange 15 and connected by way of center-conductor coupling 16. Intermediate flange 17, which includes a dielectric window 18, affords a needed liquid-tight seal of the coaxial sub assembly 10a Without blocking passage of electromagnetic energy. For purposes explained further later herein, the side walls 13a of outer conductor 13 underlying the D.-C. magnet winding 11 are constructed of a substantially non-magnetic material having a relatively high electrical resistance, such as stainless steel, while the interior of these walls carries a thin coating, 19, of material having good electrical conductivity, preferably silver.

Hollow ferrite cylinder 20 is disposed within the line section 13a concentrically with, but slightly separated from, the inner and outer conductors. Ferrite materials well known in other uses where the operating modes are different are applicable in practice of the present invention as well, and one suitable ferrite for construction of cylinder 20 is a magnesium manganese type with aluminum substitution. Other ferrites useful in microwave apparatus may be of nickel-cobalt, manganese, or manganese-zinc compositions, for example. Dielectric constant of the hollow ferrite cylinder may be about 11.0, and its permeability is a variable which can be regulated over a relatively wide range of about 1.6 to 2.4 by regulating the magnetic field intensity of the field developed by solenoid winding 11. D.-C. terminals 21 couple electrical excitation to this winding for the purpose of setting up a generally axial magnetic field which is substantially parallel with the elongated ferrite and threads it longitudinally. Adjustment of current in the solenoid winding 11 is found to effect variation in the effective electrical length of the line section, and variations of about 40% in effective length are readily made. Adjustment of current is made externally by known forms of equipment (not shown) coupled with the supply terminals 21. Switching effects are achieved by causing the line section to assume either: (1) an effective electrical length of an integral multiple of 180 degrees (one-half wavelength at the frequency involved in transmission along cable 6) or, (2) a distinctly different effective length which produces a resonance with auxiliary stub 9 at the frequency of transmission which is involved. The former condition is one which produces a positive short circuit across transmission line 6 and thereby blocks the passage of microwave energy. The latter condition, involving resonance with stub 9, effects an open-circuited state which permits the microwave energy to be transmitted. This exploitation of stub 9 avoids need for more extensive changes in control current (and in the effective electrical length of line section 10) which might otherwise be required were the effective lengths of line section 10 alone relied upon to develop shifts in switching states. Stub 9 is preferably of a simple shorted type, in which the shorting plate 22 is connected with the outer con-ductor 23 and inner conductor 24 at the end more remote from the junction with coaxial line 6.

The changes in switching states must occur with exceptional rapidity for certain purposes; so quickly, in fact, that the mutual impedance effects of outer coaxial conductor 13a would tend to produce an undesirably low time constant in the electrical circuitry including solenoid coil 11. Such a low time constant would inhibit rapid switching, and it is for this reason that outer conductor 13a is fabricated of stainless steel the relatively high resistance of which minimizes the unwanted mutual impedance effects. Silver plating 19 on the interior of this conductor suffices to minimize losses at microwave frequencies, because of the surface or skin effects which predominate, while not producing a high mutual impedance condition with coil 11.

Unfortunately, ferrite materials tend to be highly temperature-sensitive and thereby cause the effective lengths of the associated line sections to vary intolerably in the operating environments associated with high-power microwave switching. This disturbs the eflicacy of switching, and is to be avoided. The FIGURE 1 system overcomes this ditficulty by preserving the ferrite cylinder 20 within about two or three degrees centigrade of a desired temperature, ultilizing perchlorethylene as a temperatureregulating fluid. Perchlorethylene is a dielectric, a characteristic which is essential to proper functioning of the line section, and the value of this dielectric is then of course taken into account in calculations of line section lengths. This liquid fills the interior of line section 10a, and its circulation is in a substantially axial direction, between the inlet and outlet coupling pipes 25 and 26. The flow brings the liquid into intimate heat-exchange relationship with the ferrite, such that temperature of cylinder 20 is preserved substantially constant at a predetermined value. Such temperature regulation involves more than a mere cooling, and requires that there be servo control. One suitable regulating arrangement is shown to an external heat-exchanger 27 through which the coolant liquid is circulated by a pump 28 for purposes of releasing more or less thermal energy to the ambient air which is forced through it by a motor-driven blower 29. A particularly noteworthy feature of this regulating arrangement is that the dielectric coolant is in a wholly closed recirculation loop, whereby problems of supply and contamination are avoided. It should be recognized, also, that the thermal energy required to elevate the liquid to a high temperature to which it can then be closely regulated is derived from the operating electrical losses appearing as heat in the line section 10a, rather than from an auxiliary heat source. Control of the rate at which heat-exchanger 27 yields thermal energy is shown to be exercised by a louver array 30 which is actuated by a motor 31 through a mechanical coupling 32 in response to signals from a servo amplifier 33. The latter responds to the output signals from a temperature detector 34, which may be of a conventional type and which sens-es temperature of the perchlorethylene as it leaves the line section 10a, and responds further to feedback signals supplied by a pick-off device 35 of a conventional type which characterizes the louver condition at any moment. Upon a sensed increase in temperature above a predetermined value, amplifier 33 responds to actuate the louvers to a more opened condition, as monitored by the pick-off output, and upon decrease in temperature the operation is reversed in sense. The predetermined temperature to which the ferrite cylinder is held in this manner is selected to lie well below the boiling point of the perchlorethylene.

Theequipment in FIGURE 2 is designed to switch electromagnetic energy from a transmitter 36 to one or the other of the two antenna loads, 37 and 38, within a period of a few milliseconds. This switching involves a pair of variable-reactance shorting and unshorting units, 37a and 38b, respectively, which are of generally the same construction as that of line section 10 in FIGURE 1. Therefore, for convenience in disclosure, those parts which are functionally the same as corresponding parts of the line section 10 are identified by the same reference characters, with distinguishing subscripts a and b added. When the electrical current in coil 11a is adjusted to establish an electrical length of shorted switching stub 37a which at junction 39 appears as substantially one-half wavelength at the frequency of the power output from transmitter 36, and when the electrical length exhibited at junction 40 by shorted stub 38b is substantially onequarter wavelength at the same frequency, the power output applied to coaxial cable'41 by transmitter 36 is passed to antenna load 38 along coaxial line branch 42 and is blocked in attempted passage to antenna load 37 along coaxial line branch 43. In this connection, it should be noted that the junctions of the switching stubs 37a and 38b with the associated branches 42' and 43 are each onequarter wavelength (or an odd multiple thereof) displaced from the junction 44 of these branches with the output cable 41. When current in coil 11b of switching stub 38b is changed to increase its electrical length to a half wavelength, and when the current in cell 11a of stub 37a is simultaneously changed to reduce the electrical length of stub 37a to a quarter wavelength, then the full power of transmitter 36 is delivered solely to load 37. Immediate switching of power between loads 37 and 38 is accomplished simply by alternately changing the currents in switching stubs 37a and 38b to the alternate levels which establish the different quarterand half-wavelength effective lengths. Transmitter 36 may be disconnected from the lines, or rendered inactive, during the brief switching periods, such that slight mismatches in this system would not be troublesome. Unidirectional currents for the switching control of switching stubs 37a and 38b are derived from the respective power supplies 45 and 46, the current outputs of which are adjusted by regulating devices 45a and 46a, respectively, of known construction which are preferably wholly electronic (such as thyratron devices) andcan therefore operate with exceedingly high speed and precision.

With current commercial ferrite materials, the materials, the order of isolation which can be achieved at ultra high frequencies by an arrangement such as that of FIGURE 2 is about 33 db. Additional isolation or increased bandwidth for a given minimum isolation may be obtained, however, by adding further variable-reactance line sections, as shown in the block and schematic diagram in FIGURE 3. Transmitter 47 there delivers its microwave output to one of two antenna'loads 48 and 49 at any instant, via the main coaxial transmission line 50 and either of the two branch coaxial transmission lines 51 and 52. At quarter-wavelength (or odd multiples of quarter-wavelength) positions along the branch lines 51 and 52 are joined the ferrite switching line sections 51a-51c and 52a52c, respectively. These line sections are preferably of the same construction as that of line section in FIGURE 2. Each added pair of switching line sections increases the isolation by a given amount, at a given frequency. Therefore, when 33 db. of isolation is obtained through use of line sections 5111 and 52a alone, an additional 33 db. of isolation obtains upon introduction of sections 51b and 5211, a still further 33 db. of isolation obtains upon introduction of sections 510 and 520, and so forth. All of the switching line sections in each of the branches must have their switching coils energized in the same manner at any moment, of course.

In FIGURE 4 a single power source, transmitter 53, serves the multiple loads 54-57, one at a time, under control of the switching line sections 54a-57a, respectively. The latter sections are of the construction already described with reference to line section 10 in FIGURE 2, and it will also be understood that a number of such sections may be introduced into each of the branch lines feeding the loads, for purposes of increasing isolation and bandwidth of isolation. As the power output is successively switched from one to another of the loads, the solenoid coil current for control of ferrite permeability is changed only in the switching line section the load of which is under power and in the switching line section the load of which is to receive the power.

Operating frequencies of apparatus practicing these teachings may remain somewhat limited, within given bands, or alternatively, may be made adjustable. For the latter purposes, it is of course necessary that good tuning be preserved in the various transmission line sections which are to have quarter-wavelength characteristics, such as the quarter-wavelength sections in the branches along which the switching stubs are joined in FIGURES 2, 3 and 4. Conventional line stretchers (adjustable sections of transmission line) which are useful for this tuning may be either manually or remotely controlled and may be inserted into the line sections, for example. Similarly, such line stretchers may also be connected with the switching stub units, such as units 37a and 38b in FIG URE 2, to insure that the ilk/4 or (n |1))\/4 relationships identified in FIGURE 2 are maintained at different frequencies. Further, the levels of D.-C. current in the magnetizing coils of the switching stubs may be readily adjusted with conventional equipment to give the optimum changes in permeability for switching at various frequencies, if this is desired.

The embodiment depicted in FIGURE 5 is particularly advantageous in that it obviates the need for quarterwave sections intermediate the position at which a branch transmission line is fed and the position at which the variable switching reactances are introduced. Power input from a main coaxial cable 58 is there diverted to either of two loads 59 and 60 by a series arrangement for switching. Inner conductor 61 of main cable 58 is connected both to the inner conductor 62 of a first line switching section 63 and to the inner conductor 64 of a branch coaxial line 65 serving one of the loads. Outer conductor 66 of the main coaxial power cable 58 is connected to the inner conductor 67 of the second branch coaxial line 68 serving the other of the loads. This same outer conductor, 66, serves as the inner conductor of a second coaxial line switching section 69. Switching sections 63 and 69 each include a hollow ferrite cylinder, 70 and 71, respectively, and a solenoid control winding, 72 and 73, respectively, and are sealed by dielectric barriers 74 and 75, respectively, so that they may conduct dielectric fluid for temperature regulation purposes, all according to explanations earlier given with reference to the switching section 1 0 in FIGURE 1-. Outer conductors of the coaxial lines 63, 65, 69 and 68 are connected at the illustrated junction, and the electrical effects at high frequencies involve the coupling of power to one or the other load as the two switching line sections are alternately caused to assume effective lengths of one-quarter or one-half wavelength at the power frequency. The latter occurs as the current levels in the solenoid control windings 72 and 73 are alternated.

It is to be understood that while specific preferred embodiments of this invention have been illustrated and described, these disclosures are intended to be of a descriptive rather than a limiting nature, and it is contemplated that various changes, combinations, substitutions or modifications may be made in accordance with these teachings without departing either in spirit or scope from this invention in its broader aspects.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for selectably switching between substantially shorted and unshorted conditions along a highfrequency transmission line at a predetermined frequency comprising an elongated shorted line section connected in energy-exchange relationship with said transmission line at a predetermined position, an elongated ferrite member disposed between the conductive surfaces of said shorted line section, said ferrite member being of a crosssection less than that between the conductive surfaces of said section, means sealing said line section liquid-tight and including dielectric sealing means at the junction between said line section and transmission line, a dielectric liquid filling the sealed line section and contacting said ferrite member in heat-exchange relationship therewith, means for guiding flow of said dielectric liquid between said conductive surfaces of said shorted line section and in heat-exchange relationship with said ferrite member, an electrical winding about the exterior of said line section for applying to said ferrite member a D.-C. magnetizing field of an intensity which varies the permeability of said ferrite member and, thereby, the reactance of said line section sufliciently to effect a significant change in effective electrical length of said line section, a source of D.-C. excitation for said winding, means for selectably switching the D.-C. rurrent in said winding between alternate levels at which said ferrite member is differently magnetized and said line section has a first effective electrical length at said frequency which presents substantially a short circuit to said transmission line when the current in said Winding is at one of said levels and has a second efiective electrical length at said frequency which presents a high impedance to said transmission line at said 7 positionwhen the current insaid winding is at the other of said levels, the structural material of the exterior 0t said line section being of relatively high electrical resistivity to minimize its mutual impedance with said winding, a thin coating of material of relatively low electrical resistivity lining the interior surfaces of the material having high resistivity to form conductive surfaces of said line section, a liquid-circulation pathoutside of said line section connected in series with said sealed section and with a heat-exchanger to form a closed loop for circulation of said liquid through said guiding means, means for forcing said liquid through said loop, and means including said heat-exchanger preserving the temperature of said dielectric liquid at a substantially constant value.

2. Apparatus for selectabl'y switching as set forth inclaim 1 wherein said dielectric liquid is perchlorethylene, wherein said structural material includes stainless steel, and wherein said thin coating comprises a plating of'silver along the interior surfaces of said structural material.

3. Apparatus for selectably switching as set forth in claim 1 wherein said heat exchanger comprises a radiator exposed to ambient air, and wherein said means preserving the temperature of said dielectric liquid at a substantially constant value comprises a temperature detector responsive to temperature of said liquid, and" means responsive to said temperature detector forcing air through said heat-exchanger at rates to preserve the temperature of said liquid, and hence the temperature. of said ferrite member, substantially constant.

References Cited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Johnson: Ferrite Phase Shifter for the. UHF Region, Transactions on'MicroWave. Theory and Techniques,, vol. MTT7,;-N0-. 1, January 19-59, pages 27-31.

HERMAN KARL SAALBACH, Primary Examiner.

BENNETT G; MILLER, Examiner 

1. APPARATUS FOR SELECTABLY SWITCHING BETWEEN SUBSTANTIALLY SHORTED AND UNSHORTED CONDITIONS ALONG A HIGHFREQUENCY TRANSMISSION LINE AT A PREDETERMINED FREQUENCY COMPRISING AN ELONGATED SHORTED LINE SECTION CONNECTED IN ENERGY-EXCHANGE RELATIOHSHIP WITH SAID TRANSMISSION LINE AT A PREDETERMINED POSITION, AND ELONGATED FERRITE MEMBER DISPOSED BETWEEN THE CONDUCTIVE SURFACES OF SAID SHORTED LINE SECTION, SAID FERRITE MEMBER BEING OF A CROSSSECTION LESS THAN THAT BETWEEN THECONDUCTIVE SURFACES OF SAID SECTION, MEANS SEALING AND LINE SECTION LIQUID-TIGHT AND INCLUDING DIELECTRIC SEALING MEANS AT THE JUNCTION BETWEEN SAID LINE SECTION AND TRANSMISSION LINE, A DIELECTRIC LIQUID FILLING THE SEALED LINE SECTION AND CONTACTING SAID FERRITE MEMBER IN HEAT-EXCHANGE RELATIOHSHIP THEREWITH, MEANS FOR GUIDING FLOW OF SAID DIELECTRIC LIQUID BETWEEN SAID CONDUCTIVE SURFACES OF SAID SHORTED LINE SECTION AND IN HEAT-EXCHANGE RELATIOHSHIP WITH SAID FERRITE MEMBER, AN ELECTRICAL WINDING ABOUT THE EXTERIOR OF SAID LINE SECTION FOR APPLYING TO SAID FERRITE MEMBER A D.-C. MAGNETIZING FIELD OF AN INTENSITY WHICH VARIES THE PERMEABILITY OF SAID FERRITE MEMBER AND, THEREBY, THE REACTANCE OF SAID LINE SECTION SUFFICIENTLY TO EFFECT A SIGNIFICANT CHANGE IN EFFECTIVE ELECTRICAL LENGTH OF SAID LINE SECTION, A SORUCE OF D.-C. EXCITATION FOR SAID WINDING, MEANS FOR SELECTABLY SWITCHING THE D.-C. RURRENT IN SAID WINDING BETWEEN ALTERNAL LEVELS AT WHICH SAID FERRITE MEMBER IS DIFFERENTLY MAGNETIZED AND SAID LINE SECTION HAS A FIRST EFFECTIVE ELECTRICAL LENGTH AT SAID FREQUENCY WHICH PRESENTS SUBSTANTIALLY A SHORT CIRCUIT TO SAID TRANSMISSION LINE WHEN THE CURRENT IN SAID WINDING IS AT ONE OF SAID LEVEL AND HAS A SECOND EFFECTIVE ELECTRICAL LENGTH AT SAID FREQUENCY WHICH PRESENTS A HIGH IMPEDANCE TO SAID TRANSMISSION LINE AT SAID POSITION WHEN THE CURRENT IN SAID WINDING IS AT THE OTHER OF SAID LEVELS, THE STRUCTURAL MATERIAL OF THE EXTERIOR OF SAID LINE SECTION BEING OF RELATIVELY HIGH ELECTRICAL RESISTIVITY TO MINIMIZE ITS MUTUAL IMPEDANCE WITH SAID WINDING, A THIN COATING OF MATERIAL OF RELATIVELY LOW ELECTRICAL RESISTIVITY LINING THE INTERIOR SURFACES OF THE MATERIAL HAVING HIGH RESISTIVITY TO FORM CONDUCTIVE SURFACES OF SAID LINE SECTION, LIQUID-CIRCULATION PATH OUTSIDE OF SAID LINE SECTION CONNECTED IN SERIES WITH SAID SEALED SECTION AND WITH A HEAT-EXCHANGER TO FORM A CLOSED LOOP FOR CIRCULATION OF SAID LIQUID THROUGH SAID GUIDING MEANS, MEANS FOR FORCING SIAD LIQUID THROUGH SAID LOOP, AND MEANS INCLUDING SAID HEAT-EXCHANGER PRESERVING THE TEMPERATURE OF SAID DIELECTRIC LIQUID AT A SUBSTANTIALLY CONSTANT VALUE. 